Magnetic amplifier utilized as a static constant current regulator



Aug. 13, 1968 J. B. URI ETAL 3,397,361

MAGNETIC AMPLIFIER UTILIZED AS A STATIC CONSTANT CURRENT REGULATOR AFiled Jan. v, 1965 Fi- 51.2- P-:275. E.

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United States Patent O 3,397,361 MAGNETIC AMPLIFIER UTILIZED AS A STATICCONSTANT CURRENT REGULATOR Joseph Ben Uri, Michael S. Erlicki, and DavidSchieber,

Haifa, Israel, assignors to Technion Research and Development FoundationLtd., Haifa, Israel, a corporation of Israel Filed Jan. 7, 1965, Ser.No. 424,058 4 Claims. (Cl. 330-8) ABSTRACT OF THE DISCLOSURE A constantcurrent regulator in which a saturable magnetic core having arectangular hysteresis characteristic is biased to negative saturationby a control current through a control winding with load current througha load winding opposing the ampere turns of the control winding. Theload current fiows to the load through a rectifier and saturates thecore in a positive direction at the end of the load current cycle.

This invention relates to current stabilising devices.

It is known to employ magnetic amplifiers for the purpose of obtaining astabilised or constant current output and for this purpose the magneticamplifier is provided with a rather complicated external feed-backcircuit by means of which constancy in current output is achieved.

It is an object of the present invention to provide a new and improvedcurrent stabilising device which does not involve the provision of suchcomplicated circuitry.

If reference is made to FIG. l of the accompanying drawings which showsthe characteristic of a conventional self-excited magnetic amplifier, itwill be seen how this characteristic shows the variation of outputcurrent with control current for a fixed value of input voltage and loadresistance.

With a normal self-excited magnetic amplifier the portion of acharacteristic which is of most interest is the portion b-c wherein asubstantially linear rise in output current occurs for relatively smallchanges in control current. It has been noticed, however, that withvariation in the voltage or the load resistance the portions of curvea-b-c vary whilst the portions of the curve c-d-e remain substantiallyinvariant.

This phenomenon has been utilised in the present invention by the designof an electromagnetic reactor having the construction of a magneticamplifier but which is designed for operation in non-saturationconditions. Such a reactor will hereinafter be referred to as anelectromagnetic reactor of the kind specified. With an electromagneticreactor of the kind specified particular advantage can be taken of thesubstantially invariant portion c-d-e whilst the other portions c-b-acan be virtually ignored.

According to the present invention therefore there is provided a currentstabilising device comprising at least one electromagnetic reactor ofthe kind specified having an ampere-turn-ratio lying within the range of0.5 to 10.

Preferably the ampere-turn-ratio is substantially equal to one.

With such a current stabilising device a substantially constant currentcharacteristic is obtained within a very wide rang of voltage and loadvariations when the or each reactor is operated with negative controlcurrent.

Current stabilising devices of the present invention will now bedescribed with reference to FIGS. 2 to 4 of the accompanying drawings inwhich FIG. 2 is a schematic circuit diagram showing the use of a singleleg reactor of magnetic amplifier construction as a current stabilisingdevice.

3,397,361 Patented Aug. 13, 1968 F. ICC

FIG. 3 is a graphical representation of the current in the power or loadcircuit of the device of FIG. 2 plotted against the phase of thealternating voltage fed to the power circuit of the device, and FIG. 4is a schematic diagram showing the use of a bridge type of reactor ofmagnetic amplifier construction as a current stabilising device.

The device of FIG. 2 includes a saturable reactor 1 comprising a controlwinding 2 and a power winding 3 wound on a suitable saturable core (notshown). A choke 4 is in series with the winding 2. Direct currentvoltage is applied to terminals 5 the polarity being as shown. The powerwinding 3 is connected in series with a rectifier 6 and a load 7schematically represented as a resistance. The winding 3 is fed withalternating voltage applied to terminals 8.

If it is assumed that the magnetisation characteristic of the coreapproximates a rectangular or a square loop and that theinductance ofthe choke 4 is very high so that only a direct current can flow throughthe winding 2, it can be shown to first orders of approximation that theflow of current in the load circuit can be represented by the followingequation:

iag- %;(Ic`i-Ica) where:

z'a is the average load current in the load circuit Nc is the number ofturns of the control winding 2 Na is the number of turns of the powerwinding 3 Ic is the control circuit direct current Ics is the controlcircuit saturation current.

In the graph of FIG. 3 wt is the phase angle of the alternating voltageV= V0 sin (wt) applied to the terminals 8; A is the phase angle at thepoint in the cycle at which desaturation conditions occur in the core;and B is the phase angle at the point in the cycle at which the core isresaturated.

From the graph it will be seen that in the part of the cycle between thephase angles A and B the current flow through the winding 3 issubstantially constant and the core is unsaturated. At the angle B thecore resaturates. However, at this instant the rectifier 6 blocks andprevents the fiow of saturation current so that the current flow rapidlydrops to zero and remains at zero until the alternating voltage cyclerecommences. In other words, when high ampere turns in the negativedirection are present in the circuit of FIG. 2 it is possible to obtaina direct current fiow which is not limited by the inductance of thewinding 3 and which flows in the direction of rectifier conduction. Themagnitude of this load current is given by the above equation and is notdetermined by the lload resistance. This means that by operating thedevice shown in FIG. 2 in the unsaturated mode with a negative controlcurrent the device acts as a constant current device producingstabilised direct current from the alternating input fed to terminals 8.The extent of the unsaturated part of the cycle is determined by themagnitude of the saturation phase angle spread of A to B.

Since in practice A cannot be made equal to zero the circuit of FIG. 2has limitations as regards efiiciency.

The efficiency of the device is increased by effectively combining twoof the devices of FIG. 2 to produce a bridge arrangement as shown inFIG. 4.

Referring to FIG. 4 there are shown two control windings 9 and 10 andtwo power windings 11 and 12. The control windings 9 and 10 and thechoke 20 are connected in series with the control signal input terminals13 to which are connected the Ipositive and negative terminals of acontrol signal supply.

ing current power input being fed to terminals 18 which are connected tothe power windings 11 and 12 in parallel. A lead 19 is connected acrossthe power windings 11 and 12,

During each half cycle of the alternating voltage applied to theterminals 18 each reactor leg or winding pair 9, 12 and 10, 11, operatessubstantially as the arrangement of FIG. 2. However, an overlap in thecycles of operation of the two legs is caused by the fact that onreversal of phase the rectifier 16 through which positive current fiowscan pass the negative going current so long as its magnitude is smallerthan that of the positive current. As the flow of current in winding 11is limited by its resistance the current through the load circuitsupplies ampere turns in opposition to the constant ampere turns in thecontrol circuit so that by the time the rectifier 16 blocks the core ofwindings 10 and 11 is not saturated. This particular sequence of eventsin practice leads to an improvement in the constancy of the currentoutput of the device of FIG. 4.

The electrical reactors of FIGS. 2 and4 have been specifically designedso as to have ampere turn ratios substantially equal to one. It will beappreciated that with such a construction the arrangement is notsuitable for use as a conventional magnetic amplifier and does notoperate in the saturated region of the cores.

With the devices as described above it has been found that very constantcurrent characteristics can be obtained within a very wide range ofvoltage and load resistance variations.

In `an alternative circuit arrangement (not shown) a portion of the loadcurrent can be fed lback'to the control signal input to windings 9 and10 so as to constitute at least a part Vof the control signal current.

It will be appreciated that whilst the invention has been specificallydescribed with reference to a bridge connection the invention is equallyapplicable to other reactor connections such as parallel, series, andmulti-base connections.

What we claim is:

1. A constant current regulator comprising a saturable magnetic corehaving a lirst and second winding, a control current circuit, and a loadcircuit; said control circuit comprising a source of 'D-C currentconnected in series 'with said first winding; said load circuitcomprising a source of A-C current, a diode and a load connected inclosed series relation with said source of A-C current; said firstwinding 'being lwound on said core whereby D-C current through saidiirst winding tends to cause flux change in said core in a firstdirection; said second winding being wound on said core whereby currentliow in the forward direction of said rectifier yand through said secondwinding tends to cause afiux change in said core in a direction oppositeto said first direction; said load current having a peak value equal tothe product of the ratio of number of turns of said first winding to thenumber of turns of said second Winding and the D-C current through saidlirstvwindin'g; said ratio being in the range of from 0.5 to 10.

2. The device of claim 1 wherein said -ratio is one.

3. The device of claim 1 which includes inductance means connected inseries with said control circuit.

4. The device of claim 1 which includes feedback circuit means connectedbetween said load circuit land said control circuit.

References Cited UNITED STATES PATENTS 2,909,723 10/ 1959 Scorgie 330-8X 2,93 8,158 v5/ 1960 Lehtohen 330-8 X 3,138,753 6/1964 Covert 330--8 XROY LAKE, Primary Examiner. NATHAN KAUF MAN, Assistant Examiner.

